Designs for what will be Britain's biggest piece of public art, a 120 metres tall looping tower by the artist Anish Kapoor that people will be able to climb, giving spectacular views of London, were unveiled today by Boris Johnson, mayor of London.

Kapoor's Orbit, a vast, snaking steel structure, will dominate the 2012 Olympic park. It is being hailed as London's answer to the Eiffel tower and is part of an ambition to make the Olympics site a permanent visitor attraction.

Kapoor won the commission from a shortlist of bidders believed to include the artist Antony Gormley and the architects Caruso St John. Johnson said of Kapoor: "He has taken the idea of a tower and transformed it into a piece of modern British art. It would have boggled the minds of the Romans. It would have boggled Gustave Eiffel."

An artist's impression of Anish Kapoor's giant work of public art planned for the London Olympic park. Photograph: PR

The structure will officially be called the ArcelorMittal Orbit, after steel magnate Lakshmi Mittal, the richest man in Europe, who is funding it. Johnson said that if he and Mittal had not bumped into each other in a Davos cloakroom "we would not be where we are today".

Mittal said: "This project is an incredible opportunity to build something really spectacular for London, for the Olympic games, and something that will play a lasting role in the legacy of the games."

The structure will cost about £19.1m. Johnson said: "Of course some people will say we are nuts – in the depths of a recession – to be building Britain's biggest ever piece of public art. But both Tessa Jowell [Olympics minister] and I are certain that this is the right thing for the Stratford site, in games time and beyond."

Kapoor has collaborated on the project with his friend Cecil Balmond, one of the world's leading structural engineers. Approximately 1,400 tonnes of steel will be used. The plan is for work to begin soon with a completion date of December 2011.

Kapoor said one of his references was the Tower of Babel. "There is a kind of medieval sense to it of reaching up to the sky, building the impossible. A procession, if you like. It's a long winding spiral: a folly that aspires to go even above the clouds and has something mythic about it."